Working with Databases - Java 8 Recipes - page 455

+ rs.getString(3) +
" - " + rs.getString(4));
}
} catch (SQLException ex) {
ex.printStackTrace();
}
First, you can see that the Connection object is used to instantiate a Pre-
paredStatement object. The SQL string is passed to the PreparedStatement
object's constructor on creation. Since the PreparedStatement is instantiated
within the try-with-resources construct, it will be automatically closed when it
is no longer in use. Next, the PreparedStatement object is used to set values for
any substitution variables that have been placed into the SQL string. As you can see,
the PreparedStatement setString() method is used in the example to set
the substitution variable at position 1 equal to the contents of the recipeNumber
variable. The positioning of the substitution variable is associated with the placement
of the question mark ( ? ) within the SQL string. The first question mark within the
string is assigned to the first position, the second one is assigned to the second position,
and so forth. If there were more than one substitution variable to be assigned, there
would be more than one call against the PreparedStatement , assigning each of
the variables until each one has been accounted for. PreparedStatement s can ac-
cept substitution variables of many different data types. For instance, if an int value
were being assigned to a substitution variable, a call to the setInt(position,
variable) method would be in order. See the online documentation or your IDE's
code completion for a complete set of methods that can be used for assigning substitu-
tion variables using PreparedStatement objects.
Once all the variables have been assigned, the SQL string can be executed. The
PreparedStatement object contains an executeQuery() method that is used
to execute a SQL string that represents a query. The executeQuery() method re-
turns a ResultSet object, which contains the results that have been fetched from the
database for the particular SQL query. Next, the ResultSet can be traversed to ob-
tain the values retrieved from the database. Again, positional assignments are used to
retrieve the results by calling the ResultSet object's corresponding getter methods
and passing the position of the column value that you want to obtain. The position is
determined by the order in which the column names appear within the SQL string. In
the example, the first position corresponds to the RECIPE_NUMBER column, the
second corresponds to the RECIPE_NAME column, and so forth. If the recipeNum-